In general, an air-conditioner carries out the steps of compressing a coolant into a high-temperature high-pressure gaseous coolant by a compressor, passing the gaseous coolant through a condenser to produce a high-pressure mid-temperature liquid coolant, reducing pressure to form a low-temperature low-pressure liquid coolant, passing the liquid coolant through an evaporator to absorb indoor heat sources and vaporizing the coolant to complete a heat exchange, and finally passing the gaseous coolant into compressor before carrying out the next cycle, and the cycles are carried out repeatedly to providing the air-conditioning effect for an indoor environment.
The compressor of the air-conditioner is driven by a motor. For power saving and carbon reduction, the compressor of the air-conditioner is gradually developed and changed from the past AC motor to the present variable frequency DC brushless motor, and a variable voltage and variable frequency method is used for linearly controlling the rotation of a motor to control the compressor to adjust the compression level of the coolant, so as to maintain the indoor temperature within a predetermined temperature range easily without requiring the ON and OFF operation modes of the conventional AC motor. Under the control of the conventional AC motor, the controlled indoor temperature different is large, and the frequent switch between the ON and OFF operation modes consumes much energy. The difference between the two power sources resides on that the DC brushless variable frequency motor needs to convert an alternate current (AC) supplied by the grid AC power into a direct current (DC), and then achieve the effect of linearly controlling the motor rotating speed by the variable-voltage-variable-frequency inverter, but the conventional AC motor directly receives the AC power supplied by the grid AC power.
As the awareness of energy crisis arises, the renewable energy resources including solar energy, wind power, hydraulic power and geothermal heat are developed continuously to supply power to electric appliances. Therefore, partially or fully using a green energy source as a power source of the high power-consuming air-conditioner definitely helps us to save energy and lower the expense of electricity.
However, the conventional air-conditioner using the DC type of the green energy source such as solar power requires a charger to store the energy into a battery, an inverter for converting DC into AC with the same voltage & frequency (60 Hz) of the utility power grid (AC Grid), and an automatic transfer switch (ATS) is needed for switching between the utility power and the green energy source to prevent any conflict between the two sources, the AC generated by the inverter and the AC of the utility power grid are connected. In such arrangement, the battery life is a concern of system reliability and too many steps of the energy conversion resulting in low efficiency of utilizing the green energy source.